The long-range objective of this research program is to identify and characterize distinct subtypes of reading disability. To accomplish this objective, we are developing and obtaining measures from 150 reading-disabled children and 150 matched controls on a broad array of behavioral processes which are theoretically or empirically related to reading disability. The research is being conducted by four testing domains. Academic and Cognitive Abilities are being evaluated by a battery of standardized achievement, language, and intelligence tests. These data will provide longitudinal information on previously tested Colorado Family Reading Study subjects, as well as information concerning the effectiveness of the tests as diagnostic instruments. Word Decoding Operations are being evaluated by several techniques including analyses of spelling errors, oral reading errors, and eye fixation patterns. Cerebral Specialization is being studied with recently developed physiological techniques in combination with traditional behavioral measures. The measurement of cortical evoked potentials will provide information on patterns of hemispheric dominance in processing different types of information. Finally, Genetic Linkage Analyses are being conducted on a limited number of families whose members exhibit patterns of reading disability which strongly suggest genetic influence. Pilot testing has been completed, and the testing of core subjects has been initiated.